1. Field of the Invention
This invention relates to a condenser and an air conditioning refrigeration system using the condenser, and more particularly to, a condenser preferably used for an automobile air conditioning refrigeration system and an air conditioning refrigeration system using the condenser.
2. Description of Related Art
An automobile air conditioning refrigeration system is usually a vapor compressing system including a compressor, a condenser, an expansion valve and an evaporator.
A refrigerant state in such a refrigeration cycle is shown in FIG. 22 which shows a Mollier diagram having a vertical axis representing a pressure and a horizontal axis representing an enthalpy. In the diagram, the refrigerant is in a liquid phase in the left hand area of the liquid phase line, in a mixed phase including gas and liquid in the area between the liquid phase line and the vapor phase line, and in a vapor phase in the right hand area of the vapor phase line.
As shown in the solid line in FIG. 22, the refrigerant compressed by the compressor changes its status from the point A to the point B, resulting in a high-temperature and high-pressure gaseous refrigerant. Then, the gaseous refrigerant cooled by the condenser changes its status from the point B to the point C, resulting in a liquified refrigerant. Next, the liquified refrigerant is decompressed and expanded by the expansion valve to change its status from the point C to the point D, resulting in a low-pressure and low-temperature refrigerant in a mist or a gaseous state. Further, the refrigerant is evaporated by exchanging heat with ambient air in the evaporator to change its status from the point D to the point A, resulting in a gaseous refrigerant. The enthalpy difference between the point D and the point A corresponds to a heat quantity for cooling ambient air. The larger the enthalpy difference is, the larger the refrigeration ability is.
Conventionally, in such a refrigeration cycle, a multi-flow type heat exchanger is well-known as a condenser for changing the refrigerant status from the point B to the point C. As shown in FIG. 23, the condenser is provided with a pair of headers 102 and a core 101. The core 101 is provided with a pair of headers 102 and a plurality of heat exchanging tubes disposed parallel to each other with the ends thereof communicated with the headers 102, 102. The plurality of heat exchanging tubes are divided into a plurality of passes P1, P2, P3 and P4 by partitions 103 provided in the headers 102. In the condenser, the refrigerant is condensed by exchanging heat with ambient air while flowing through each of the passes P1 to P4 in turn in a meandering manner.
As mentioned above, in the aforementioned refrigeration cycle, as mentioned above, the larger the enthalpy difference from the point D to the point A is, the larger the refrigeration ability is. In recent years, in the condensing process for changing the refrigerant status from the point B to the point C, a condenser which makes the enthalpy difference larger at the time of evaporation by sub-cooling the condensed refrigerant to the temperature several degrees lower than the point C to increase the heat rejection amount, has been developed.
An improved condenser having a receiver tank between the condensing zone and the sub-cooling zone has been proposed.
The condenser with the receiver tank, as shown in FIG. 24, is provided with a multi-flow type heat exchanger core 111 and a receiver tank 113 attached to one of the headers 112. An upstream portion of the heat exchanger core 111 constitutes a condensing zone 111C and a downstream portion of the heat exchanger core 111 constitutes a sub-cooling zone 111S. In this condenser, the refrigerant is condensed by exchanging heat with ambient air while flowing through each of the passes P1 to P3 of the condensing zone 111C in a meandered manner. Then, the condensed refrigerant is introduced into the receiver tank 113 to separate gaseous refrigerant and liquified refrigerant, and only the liquified refrigerant is introduced into the sub-cooling zone 111S to be sub-cooled.
In the refrigeration cycle using such a condenser, as shown in the dotted line in FIG. 22, the refrigerant compressed by the compressor changes its status from the point A to the point Bs, resulting in high-temperature and high-pressure gaseous refrigerant. Then, the gaseous refrigerant is cooled in the condensing zone 111C to change its status from the point Bs to the point Cs1, resulting in a liquified refrigerant. Furthermore, the liquified refrigerant flows through the receiver tank 113 and is sub-cooled in the sub-cooling zone 111S. Therefore, the refrigerant changes its status from the point Cs1 to the point Cs2, resulting in a perfect liquid refrigerant. Then, the liquid refrigerant is decompressed and expanded by the expansion valve and changes its status from the point Cs2 to the point Ds, resulting in a gaseous or mist refrigerant. Thereafter, the refrigerant is evaporated by the evaporator to change its status from the point Ds to the point A, resulting in a gaseous refrigerant.
In this refrigeration cycle, by sub-cooling the condensed refrigerant from the point Cs1 to the point Cs2 as shown in the diagram, the enthalpy difference (Ds to A) at the time of evaporation becomes larger than the enthalpy difference (D to A) at the time of evaporation in a normal refrigeration cycle. As a result, an excellent refrigeration effect can be obtained.
The conventional proposed condenser with a receiver tank is installed in a limited space in an engine room in the same manner as in the existing condenser shown in FIG. 23. Therefore, the size of the conventional proposed condenser with a receiver tank is basically the same as that of the existing condenser with no receiver tank. However, the lower portion of the conventional proposed condenser with a receiver tank constitutes a sub-cooling zone 111S which does not act so as to condensate the refrigerant. Therefore, the condensing zone 111C becomes smaller as compared to the existing condenser, resulting in a deteriorated condensing ability. Therefore, it is required to raise the refrigerant pressure by the compressor to send the higher-temperature and higher-pressure refrigerant to the condensing zone 111C so that the refrigerant can be assuredly condensed at such a low condensing ability. As a result, the refrigerant pressure in the refrigerant cycle, especially at the condensing zone in the refrigerant cycle, raises. As illustrated in the Mollier diagram shown in FIG. 22, in a refrigeration cycle using a conventional proposed condenser with a receiver tank, the refrigerant pressure at the condensing zone and the sub-cooling zone (Bs to Cs2) is higher than that of the normal refrigerant cycle.
As will be apparent from the above, in a conventional proposed condenser with a receiver tank, it is required to raise the refrigerant pressure, resulting in, for example, an increased load of a compressor, which in turn requires a large compressor and/or a high performance compressor. This causes a large and heavy system, resulting in a worse fuel consumption rate and an increased manufacturing cost.